I. SUMMARY OF PARENT GRANT GM067237 The proposed studies in the parent grant focus on the molecular mechanisms underlying endocytic recycling. Cells and tissues establish and maintain their unique architectures in large part through the tight regulation of protein and membrane transport. One key aspect of this process is endocytic recycling, the selective return of internalized macromolecules to the cell surface from endosomes. Recycling endosomes also contribute to macroautophagy, the process of cellular ?self-eating? required for cell survival under adverse conditions. Thus, understanding the endocytic recycling process and its role in cellular physiology is of fundamental importance to cell biology and has broad relevance to many areas of biomedicine including cancer and type II diabetes. Our general approach has been to exploit powerful features of C. elegans genetics to characterize proteins that are required for the recycling process in vivo. We then extend these findings to mammalian cells and to in vitro analysis of the relevant C. elegans proteins and their mammalian homologs. For many of these studies we focused on a system that we pioneered, the C. elegans intestine, a very simple model that allows facile analysis of endocytic membrane transport pathways within intact polarized epithelia. In new preliminary work, we have identified key new indirect links that bridge the RAB-10 GTPase to the exocyst membrane tethering complex and propose to test mechanistic models for how RAB-10 influences exocyst during recycling and autophagy. We further analyze another key recycling regulator, F-BAR protein SDPN-1/Syndapin, and identify new SDPN-1 interaction partners important for recycling function. We propose extensive new in vivo and in vitro analysis to define how Syndapin family proteins function on endosomes. Given the high level of phylogenetic conservation of such pathways from worms to mammals, and our parallel analysis in human cells, we expect that our work will provide extensive insight into key conserved elements relevant across species. This work is important for understanding disease etiology and in identifying therapeutic targets for disease intervention.